Sand blast machine for applying pressure to abrasive



F. J. HULL March 14, 1933.

SAND BLAST MACHINE FOR APPLYING PRESSURE TO ABRASIVE Filed Dec. 1.0, 1930 2 Sheets-Sheet l F. J. HULL March 14, 1933.

SAND BLAST MACHINE FOR APPLYING PRESSURE TO ABRAS IVE Filed Dec. 10, 1950 2 Sheets-Sheet 2,

Patented Mar. 14, 1933 oni'rsstares r orrics ros'rn n J. HULL, OF naennsrown, MARYLAND, AssIGNon T PANGBOR CORPORA- Tron, A oonronerron or MARYLAND v SAND BLAST IvIACHINE' FOR APPLYING PRESSURE T0 ABRASIVE Application filed. December 10, 1980. Serial No. 501,175.

The sand blast machine for applying pressure to abrasive described in my United StatesPatent No. 1,710,169 shows a tank divided into upper and lower chambers. In the operation of. this machine continuous pressure is maintained in the lower chamber, the air pressure in the upper chamber being alternately released so as to permit it to drop to atmospheric pressure so that abrasive can be introduced into this chamber and raised or increased so that the abrasive can be transferred to the lower chamber. a

In the operation of this machine there is a tendency for the bleeder valve which controls the changes of pressure in the upper chamber to become inefficient due to the expansion of the air in the lower chamber into said bleeder or control valve and even for the control or bleeder valve to become clogged with abrasive due to the backflow of air from the lower chamber. tendency to obstruction of the control valve occur when the valve is shifting from one seat to the other so that both seats are open, i. e., when the bleeder valve which operates between two seats is shifted from one seat to the other, and after it has reached its lower seat before the pressure is built up in the upper chamber.. As there is noactual loss of pressure in the lower chamber, and the period during which this back flow occurs is very short, the trouble has been very difficult to locate and analyze so that its actual correction has consumed several years of development work on this apparatus. By a rearrangement of the piping and the provision of means properly located between the lower or pressure chamber of the tank and the control valve, the difficulty referred to has been overcome, eliminating the tendency of the compressed air in the lower chamber to expand into the control valve, rendering it inoperative by raising the pressure at this point and by carrying abrasive into this valve. In this way the efiiciency of the apparatus has been greatly increased by making it'possible to lower the pressure in the upper chamber more promptly, permitting the weight of abrasive on the abrasive sup- These tendencies or the ply valve toopen this supply valve some sec-p somewhat distorted to bring them into the plane of the figure. I

Figure 2 1s a section showing the lower portion of the tank, the mixer valve'andthe relation ofthe nonreturn valve to this construction.

Referring to the drawings by numerals, each of whichisused to indicate the same or similar parts in the difi'erent figures, the construction shown comprises a sand blast 'pressure tank 1, having upper or primary chamher 2 and lower or secondary chamber 3. The two chambers are connected together for the transfer of the abrasive from one chamber to the other by an abrasive transfer passage 4: controlled .by the abrasive transfer valve 5, which as shown is brought to closed position by the air supply flow. from the pipe 6 leading to the air discharge opening 7 beneath and enclosed by the valve'5 which is in the form of a cup fitting over the discharge opening or nozzle 7. This valve is opened by the weight of the abrasive when .the pressure in the two chambers is equallized. The operation of this valve is assisted by a light spring 8 not ordinarily sufiicient to support the weight of abrasive on the valve, which tends to hold the valve near or incontact with the seat 9 surrounding the opening 4, the relatively tight closure of the valve being effected by the excess air pressure in the lower chamber 3 as compared to that in the upper chamber 2.

Abrasive is fed to the f upper chamber from the concave head of the tank at 10, Figure 1, by way of an abrasive inletlor feed passage 11- controlled by the upper or feed air is fed into the upper chamber 2, the operation of this valve being fully described in my previous patent already referred to. Air is admitted to and discharged from the upper chamber by way of the fitting described in the previous patent, which fitting is conv nected to the upper chamber of the tank by discharge or outlet passage 16 and inlet passage 17, the fitting being in turn connected double acting valve 21 supported on a stem or rod 22 connected to an actuating piston 24 in the cylinder 25, which piston is controlled by the automatically or manually operate'd controlvalve 27 which at predetermined periods connects the cylinder 25 above the piston to'the outside air to exhaust it and controls a supply of compressed air from the air main 28, said air mainbeing connected to the valve by a pipe 29, the control valve 27' being connected to the head of the cylinder 25 by an air pipe 30. The cylinder is also connected intermediately to the air supply 7 by fitting 31.

The air pressure pipe 28 is also shown as extending downwardly toward the lower chamber 3 to which it is connected by the pipe 6 previously described, which discharges into the lower chamber through the nozzle or discharge opening 7 beneath the cup valve 5.

The air pressure pipe 28 is shown as extending still further downwardly, its lower end, Figure 2, entering the mixer or mixer valve 35. In accordance with the well known practice in the operation of the continuous type of tank, the pressure in the upper tank is released from time to time permitting the valve 12 therein to be opened to admit a new charge of abrasive to this tank. This is accomplished by raising the piston 24 for which purpose the pipe 30 leading to the upper head of cylinder 25 is cut oif from the air pressure supply 28 and opened tothe atmosphere'by the operation of valve 27 When the pressure in the chamber 2 has been reduced practically to atmosphere, the valve 12 deprived of its supporting pressure is opened by the weight of the abrasive resting on it and a supply of abrasive is admitted to the upper chamber. The position of the valve 27 is then changed cutting ofi the discharge to the outside air and again connecting, the air pressure pipe 28 by Way of the pipe 30 to the upper end of the cylinder. In this way the piston 24 is moved downwardly and the valve 21 contacts the lower seat 20 leaving the upper seat 19 open for the ad mission of air under pressure from the pipe 28, which air, after passing the seat goes through the pipe 18 to the fitting 15 and hence by way of the pipe 17 to the upper chamber 2 valve 12 in a manner which can be easily un- V derstood, is fully explained 1n the previous patent. The valve 5 is then in its turn opened by the weight of abrasive thereon, the equalization of the pressure in the two tanks relieving the tendency to hold it closed against the weight of the abrasive which is then discharged from the chamber 52 into the lower chamber 3, where it is available for projection by wayof the mixing valve 35.

In the operation of the apparatusas described it has been found that the exhaust of the pressure in the upper chamber 2 is retarded or prevented and in'some instances there is even a tendency to deposit abrasive in the control valve, both of which objectionable features of the operation seem to be due to the tendency, only discovered after long and careful investigation, of the compressed air in the lower'cha'mber to expand and flow backward into the control valve 23 during the exhaust from the upper chamber when the pressure in the valve is relatively low, also that a quantity .of abrasive accumulates in the controller or bleeder valve 23 and on the seats 19 and 20, interfering with its operation.

After careful experimentation and observation for several years it has been found that this is due to the expansion and backfiow of the air from the lower chamber which sometimes expands to such an extent and gains sufficient velocity to carry the suspended abrasive from the vicinity of the abrasive valve 5'by way of the nozzle 7 the pipe 6 depositing it on the seats 20, 19 as aforesaid and in the cylinder 27. 7

After careful investigation of this difliculty included in several years work in perfecting the apparatus it has been found that by placing a check valve 40 in the pipe28 I just above the. air pressure pipe 6 leading to the nozzle 7 beneath the transfer valve 5, Figure, 1, or by placing such a check or nonreturn valve 41 in the pipe 6, Figure 2, the difficulty is completely overcome, i. e., the

expansion and backfiow of theair from the lower chamber 3 to the piston valve or bleeder valve 23 and particularly to seats '19, 20 I and to the cylinder 25. In this way the operation of this apparatus is rendered much more efiicient in that the complete exhaust of the upper chamber down to atmospheric pressure is effected more promptly without the tendency to backflow and consequent choking of the controller valve 23. .As the result of this improvement, the abrasive supe ply valve 12 opens'promptly at the end of a predetermined exhaust period admitting the supply of abrasive to the upper chamber 1 as it is required and the tendency of the compressed air in the lower chamber toexpand and choke and impede the operation of'the' cylinder valve and to carry abrasive into this valve is completely overcome and eliminated. The operation of the apparatus has been fully described in connection with the description of applicants construction as shown in the drawings.

I have thus described a continuously operating sand blast machine for applying pressure to the abrasive, embodying the features of my invention in the preferred form, the description being specific and in detail in order that the manner of constructing, operating and using the same may be clearly understood, however, the specific terms herein are used descriptively rather than in a limiting sense, the scope of the invention being defined in the claims.

WVhat I claim as new and desire to secure by Letters Patent is:

1. The combination in a sand blast machine for applying pressure to abrasive, the same comprising a tank having upper and lower chambers with valve controlled pas sages for the admission of the abrasive to the upper chamber and its transfer to the lower chamber, means introducing the air supply pressure beneath said valves tending to close the same, a double acting piston valve for controlling the inlet of air to and the exhaust from the upper chamber, an air pressure supply connected to said piston valve haustfrom the upper chamber, and air pressure supply connected to said piston valve and to said lower chamber, said connection of the pressure air to the lower chamber including sald air pressure lead to and beneath the transfer valve and a lead to the lower end of the tank including a mixing valve and means for preventing backflow by way of said air pressure pipe which discharges beneath the transfer valve. c a}. The combination in a sand blast machine for applylng pressure to abrasive, having upper and lower tanks with means for admitting the abrasive to the upper tank and transferring it from the upper to the lower tank by gravity,'means providing a supply of air under pressure means for maintaining the pressure in the lower tank and alternately applying and exhausting the pressure in the upper tank including an air pressure operated double controller valve connected to the air pressure supply and to the lower tank and means for preventing expansion of the air in the lower chamber and consequent backflow from the lower cham her into said controller valve.

Signed at Hagerstown, Maryland, this 4th day of December 1930.

FOSTER J. HULL.

and to said lower chamber, a nonreturn valve for preventing backflow from said lower chamber to said piston valve when the pressure in the upper chamber is exhausted.

2. The combination in a sand blast machine for applying pressure to abrasive, the same comprising a tank having upper and lower chambers with valve controlled passages for the admission of the abrasive to the upper chamber and its transfer to the lower chamber, means introducing the air supply pressure beneath said valves tending to close the same, a double acting piston valve for controlling the inlet of air to and the exhaust from the upper chamber, an air pressure supply connected to said piston valve and to said lower chamber, said connection comprising a pipe discharging the pressure air beneath the transfer valve as aforesaid and a connection to the bottom of the lower chamsupply pressure beneath said valves tending to close the same, a double acting piston valve for controlling the inlet of air to and the ex- 

